Duplicate extensions appearing was fixed right after 2.0 came out. It can either be downloaded from the Source Code tab above (version 2.0.0.37 on Jan 7th) ... you would need to compile the BE core to produce a new BlogEngine.Core.dll file. Or
wait till the next version of BE comes out in June.

Compiler
Error Message:CS1061: 'System.Collections.Generic.KeyValuePair<string,BlogEngine.Core.Web.Extensions.ManagedExtension>' does not contain a definition for 'Name' and no extension method 'Name' accepting a first argument of
type 'System.Collections.Generic.KeyValuePair<string,BlogEngine.Core.Web.Extensions.ManagedExtension>' could be found (are you missing a using directive or an assembly reference?)

Line 27:
Line 28: foreach (var setting in from x in ExtensionManager.Extensions
Line 29: where x.Name == extname
Line 30: from setting in x.Settings
Line 31: where !string.IsNullOrEmpty(setting.Name) && !setting.Hidden